The invention relates to optical communications networks, and more particularly relates to a protection ring architecture for such networks.
Optical transmission systems and, especially systems using Dense Wavelength Division Multiplexing (DWDM), are desirable since they provide extremely wide bandwidths for communications channels. Each communications channel in a DWDM transmission system carries a plurality of, for example, 16, 40 even 80, optical channels (wavelengths) on a single optical fiber and single optical repeater. However, there is a trade off between providing wider bandwidth communications channels, with their corresponding lower cost of transport, and their vulnerability to a large-scale disruption of communications services due to a transmission medium failure. Therefore, it is important that an optical transmission system, for example, those employing DWDM, have the capability to recover quickly from a transmission medium failure because of the impact that such a failure has on communications services.
When a node detects a transmission failure, i.e., a loss of signal (LOS), it enters a series of restoration logic steps to determine if it ought to invoke protection switching procedures, e.g., so called 1+1 or 0xc3x971 protection switching, to quickly recover from the failure. If not, then the node sends a message identifying the failure in a control (supervisory) channel to a next node. The next node similarly determines if it ought to invoke protection switching to deal with the failure. If not, then that node sends the message identifying the failure in the control channel to a next node, an so on. When a node receiving the failure message determines that it ought to invoke protection switching and does so, it then notifies the other nodes via the control channel that such protection switching has been invoked.
It can be appreciated that the above procedure is time consuming, and is especially so for those transmission systems that have to invoke protection switching as quickly as possible to meet customer expectations relating to system xe2x80x9cdown timexe2x80x9d.
We have recognized that the best way in which to route a supervisory message from one node to a next node of a transmission system is to split the control channel signal carrying the supervisory message, send one of the split control channel signals to an output via switchable apparatus for immediate transmission to the next node and send the other split control channel signal to a controller for analysis. If the controller, responsive to the supervisory message, invokes a predetermined procedure, e.g., protection switching, it then forms a supervisory message identifying the invoked procedure, operates the switchable apparatus to route the latter message to the output in place of the split control channel signal message.
These and other aspects of the invention will be appreciated from the following detailed description, accompanying drawings and ensuing claims.